We study exclusive $B_s$ decays to final states with $η$ and $η^\prime$, induced by the rare $b \to s \ell^+ \ell^-$ and $b \to s ν\bar ν$ transitions. Differential decay rates and total branching fractions are predicted in the Standard Model, adopting the flavour scheme for the description of the $η$-$η^\prime$ mixing. We discuss the theoretical uncertainty related to the hadronic matrix elements. We also consider these decay modes in a new Physics scenario with a single universal extra dimension, studying the dependence of branching ratios and decay distributions on the compactification scale $R^{-1}$ of the extra dimension.
We investigate the $ε^{\prime} /ε$ for $K\to ππ$ in a sequential fourth generation model. By giving the basic formulae for $ε^{\prime}/ε$ in this model, we analyze the numerical results which are dependent of $m_{t^{\prime}}$ and imaginary part of the fourth CKM factor, ${Im}V^{*}_{t^{'}s}V_{t^{'}d}$ (or $V^{*}_{t^{'}s}V_{t^{'}d}$ and the fourth generation CKM matrix phase $θ$). We find that, unlike the SM, when taking the central values of all parameters for $ε^{\prime}/ε$, the values of $ε^{\prime}/ ε$ can easily fit to the current experimental data for all values of hadronic matrix elements…
We provide model-independent bounds on the rates of rare decays $η(η^\prime) \to ππ$ based on experimental limits on the neutron electric dipole moment (nEDM). Starting from phenomenological $η(η^\prime) ππ$ couplings, the nEDM arises at two loop level. The leading-order relativistic ChPT calculation with the minimal photon coupling to charged pions and a proton inside the loops leads to a finite, counter term-free result. This is an improvement upon previous estimates which used approximations in evaluating the two loop contribution and were plagued by divergences. While constraints on the $η…
We investigate the exclusive rare baryonic $Λ_{b}\toΛ\ell^{+}\ell^{-}$ in a family non-universal $Z^{\prime}$ model, which is one of the natural extension of standard model. Using transition form factors, calculated in the framework of light cone QCD sum rules, we analyze the effects of polarized and unpolarized CP violation asymmetries for the said decay. Our results indicate that the value of unpolarized and polarized CP-violation asymmetries are considerable in both $Λ_{b}\toΛμ^{+}μ^{-}$ and $Λ_{b}\toΛτ^{+}τ^{-}$ channels and hence they give clear indication of new physics arising from the …
We study a new method for detecting non-universal gauge bosons $Z'$ via considering their effects on rare top decays. We calculate the contributions of the non-universal gauge bosons $Z'$ predicted by topcolor-assisted technicolor (TC2) models and flavor-universal TC2 models on the rare top decays $t\longrightarrow cV(V=g,γ,Z)$ and $t\longrightarrow cl_{i}l_{j}(l_{i}, l_{j}=τ, μ$, or $e)$. We show that the branching ratios of these processes can be significantly enhanced. Over a sizable region of the parameter space, we have $Br(t\longrightarrow cg)\sim10^{-5}$ and $Br(t\longrightarrow cττ)\si…
Meson decays offer a good opportunity to probe new physics. The rare kaon decay $K^+ \rightarrow π^+ ν\barν$ is one of the cleanest of them and, for this reason, is rather sensitive to new physics, in particular, vector mediators. NA62 collaboration, running a fixed-target experiment at CERN, recently reported an unprecedented sensitivity to this decay, namely a branching fraction of $BR(K^+ \rightarrow π^+ ν\barν) = (11^{+4.0}_{-3.5})\times 10^{-11}$ at 68\% C.L. Vector mediators that couple to neutrinos may yield a sizeable contribution to this decay. Motivated by the new measurement, we int…
Rare weak decays of $η^\prime\to Kπ$ have been investigated in the framework of the $U(3)$ chiral perturbation theory at the leading order. Our study shows that the branching ratio ${\cal B}(η^\prime\to Kπ)$ is of the order of $10^{-11}$, which is far below the present experimental upper bound given by the BESIII Collaboration. By further analysis of $η^\prime\to K^+π^-$ and $η^\prime\to K^0π^0$, the ratio of isospin amplitudes is found that $|A_{1/2}/A_{3/2}|\simeq 35$, which supports that the $ΔI=1/2$ transition enhancement, namely, the $ΔI=1/2$ rule, could be functional in $η^\prime$ weak d…
We discuss same-sign dilepton production mediated by Majorana neutrinos in high-energy proton-proton collisions $pp\ra \ell^+ \ell^{\prime +}X$ for $\ell,~ \ell^\prime = e,~ μ,~ τ$ at the LHC energy $\sqrt{s}=14$ TeV, and in the rare decays of $K$, $D$, $D_s$, and $B$ mesons of the type $M^{+}\ra M^{\prime -}\ell ^{+}\ell ^{\prime+}$. For the $pp$ reaction, assuming one heavy Majorana neutrino of mass $m_N$, we present discovery limits in the $(m_{N},|U_{\ell N}U_{\ell^\prime N}|)$ plane where $U_{\ell N}$ are the mixing parameters. Taking into account the present limits from low energy experi…
The branching ratio of the electromagnetic rare decays $η\toπ^0γγ$ and $η^\prime\to (π^0,η)γγ$ are analysed in terms of scalar and vector meson exchange contributions using the frameworks of the Linear Sigma Model and Vector Meson Dominance, respectively. The measured $η\toπ^0γγ$ process serves as a test of our approach while the non yet measured $η^\prime\to (π^0,η)γγ$ reactions are predicted for the first time. Our prediction for the $η\toπ^0γγ$ decay agrees with recent experimental reported values, thus supporting the validity of our framework. Therefore, our predictions for the $η^\prime\t…
The $η$ and $η^{\prime}$ mesons are nearly unique in the particle universe since they are almost Goldstone bosons and the dynamics of their decays are strongly constrained. The integrated $η$-meson samples collected in earlier experiments amount to $\sim10^{9}$ events. A new experiment, REDTOP (Rare Eta Decays To Probe New Physics), is being proposed, with the intent of collecting a data sample of order 10$^{14}$ $η$ (10$^{12}$ $η^{\prime}$) for studying very rare decays. Such statistics are sufficient for investigating several symmetry violations, and for searching for particles and fields be…
We investigate the rare radiative decays of extra gauge neutral bosons. In particular, we established the theoretical predictions for the production of unparticle in decays of $Z^{\prime}$ - bosons. The implementation of our prediction in the analysis at the LHC experiments should be straightforward and lead to more precise determination or limits of unparticle couplings and/or $Z^{\prime}$ couplings and masses.
Conventionally for observable $n-{\bar n}$ oscillation through Pati-Salam intermediate gauge symmetry in $SO(10)$, the canonical seesaw mechanism is also constrained by $M_R \sim M_C \le 10^6$ GeV which yields light neutrino masses much larger than the neutrino oscillation data. Recently, this difficulty has been evaded via inverse seesaw mechanism, but with proton lifetime far beyond the experimentally accessible limits. In the present work, adopting the view that we may have only a TeV scale $Z^{\prime}$ gauge boson, we show how a class of non-SUSY $SO(10)$ models allow experimentally verifi…
Flavor symmetries successfully explain lepton and quark masses and mixings yet it is usually hard to distinguish different models that predict the same mixing angles. Further experimental input could be available, if the agents of flavor breaking are sufficiently low in mass and detectable or if new physics with non-trivial flavor charges is sufficiently low in mass and detectable. The recent hint for lepton-nonuniversality in the ratio of branching fractions $B \to K μμ$ over $B \to K e e$, $R_K$, suggests the latter, at least for indirect detection via rare decays. We demonstrate the discrim…
Measuring the lepton anomalous magnetic moments $(g-2)$ and the rare decays of light pseudoscalar mesons into lepton pairs $P\to l^{+}l^{-} $, serve as important tests of the Standard Model. To reduce the theoretical uncertainty in the standard model predictions, the data on the charge and transition form factors of the light pseudoscalar mesons play a significant role. Recently, new data on the behavior of the transition form factors $P\toγγ* $ at large momentum transfer were supplied by the BABAR collaboration. There are several problems with the theoretical interpretation of these data: 1) …
The SM prediction for the ratio $\varepsilon^\prime/\varepsilon$ appears to be significantly below the experimental data. Also $\varepsilon_K$ in the SM tends to be below the data. Any NP removing these anomalies will first of all have impact on flavour observables in the $K$ meson system, in particular on rare $K$ decays and $ΔM_K$. Restricting the operators contributing to $\varepsilon^\prime/\varepsilon$ to the SM ones and to the corresponding primed operators, NP contributions are quite generally dominated either by QCD penguin (QCDP) operators $Q_6(Q_6^\prime)$ or electroweak penguin (EWP…
$SU(2)_L$-invariance links charged dilepton $\bar q\,q^\prime\,\ell^+\,\ell^-$ and dineutrino $\bar q\, q^\prime\, \barν\,ν$ couplings. This connection can be established using the Standard Model Effective Field Theory framework, and allows to perform complementary experimental tests of lepton universality and charged lepton flavor conservation with flavor-summed dineutrino observables. We present its phenomenological implications for the branching ratios of rare charm decays $c\to u\,ν\,\barν$ and rare $B$ decays $b\to s\,\barν\,ν$ decays.
Using the form factors calculated in the three-point QCD sum rules approach, we calculate the new physics contributions to the physical observables of $B_c \to D_s^* μ^+μ^-$ decay in the family non-universal $Z^{\prime}$ model. Under the consideration of three cases of the new physics parameters, we find that: (a) the $Z^{\prime}$ boson can provide large contributions to the differential decay rates; (b) the FBA could be increased by about 47%, 38%, and 110% at most in S1, S2, and ELV, respectively. In addition, the zero crossing could be shifted in all the cases; (c) when $\hat{s}>0.08$, the …
We study weak radiative $|Δc|=|Δu|=1$ decays of the charmed anti-triplett ($Λ_c$, $Ξ_c^{+}$, $Ξ_c^{0}$) and sextet ($Σ_c^{++}$, $Σ_c^+$, $Σ_c^0$, $Ξ_c^{\prime +}$, $Ξ_c^{\prime 0}$, $Ω_c$) baryons in the standard model (SM) and beyond. We work out $SU(2)$ and $SU(3)_F$-symmetry relations. We propose to study self-analyzing decay chains such as $Ξ_c^+ \to Σ^+ (\to p π^0) γ$ and $Ξ_c^0 \to Λ(\to p π^-) γ$, which enable new physics sensitive polarization studies. SM contributions can be controlled by corresponding analysis of the Cabibbo-favored decays $Λ_c^+ \to Σ^+ (\to p π^0) γ$ and $Ξ_c^0 \to…
Using the light-front quark model, we calculate the transition form factors, decay rates, and longitudinal lepton polarization asymmetries for the exclusive rare $B_s\to (K,η^{(\prime)})(\ell^+\ell^-,ν_{\ell}\bar{ν_{\ell}}$ ($\ell=e,μ,τ$) decays within the standard model, taking into account the $η-η'$ mixing angle. For the mixing angle $θ=-20^{\circ}$ ($-10^{\circ}$) in the octet-singlet basis, we obtain ${\rm BR}(B_s\to η\sumν_{\ell}\barν_{\ell})=1.1 (1.7)\times 10^{-6}$, ${\rm BR}(B_s\to ημ^+μ^-)=1.5 (2.4)\times 10^{-7}$, ${\rm BR}(B_s\to ητ^+τ^-)=3.8 (5.8)\times 10^{-8}$, ${\rm BR}(B_s\to …
We study rare leptonic decays of vector $B$ mesons in the scalar leptoquark and family non-universal $Z^\prime$ models. We constrain these new couplings by using the measured branching fractions of $B_{s,d} \to μ^+ μ^-$ processes and the existing $B_{s,d}^0-\bar B_{s,d}^0$ mixing data. We estimate the branching fractions of $B_{s,d}^* \to μ^+ μ^-$ in both the models, which are found to be reasonably enhanced from their corresponding standard model values and within the reach of Run 2-3 of LHC.
In the SUSY SO(10) GUT context, we study the exclusive processes $B \to K^{(*)} l^+l^-(l=μ,τ)$. Using the Wilson coefficients of relevant operators including the new operators $Q_{1,2}^{(\prime)}$ which are induced by neutral Higgs boson (NHB) penguins, we evaluate some possible observables associated with these processes like, the invariant mass spectrum (IMS), lepton pair forward backward asymmetry (FBA), lepton polarization asymmetries etc. In this model the contributions from Wilson coefficients $C_{Q_{1,2}}^\prime$, among new contributions, are dominant. Our results show that the NHB effe…
We summarize the presentations made within Working Group 3 of the CKM2021 workshop. This working group is devoted to rare $B$, $D$ and $K$ decays, radiative and electroweak-penguin decays, including constraints on $V_{\rm td}/V_{\rm ts}$ and $ε^\prime / ε$. The working group has thus a very broad scope, and includes very topical subjects such as the coherent array of discrepancies in semi-leptonic $B$ decays. Each contribution is here summarized very succinctly with the aim of providing an overview of the main results. The reader interested in fuller details is referred to the individual contr…
We study the full angular distribution of semileptonic rare charm baryon decays in which the secondary baryon undergoes weak decay with sizable polarization parameter, $Ξ_c^+\toΣ^+\,(\to pπ^0)\ell^+\ell^-$, $Ξ_c^0\toΛ^0\,(\to p π^-)\ell^+\ell^-$ and $Ω_c^0\toΞ^0\,(\to Λ^{0} π^0)\ell^+\ell^-$. Such self-analyzing decay chains allow for seven additional observables compared to three-body decays such as $Λ_c \to p \ell^+ \ell^-$, with different sensitivities to the $|Δc|=|Δu|=1$ weak couplings. Opportunities to test the standard model in $c \to u$ transitions with standard model null tests and ot…
We consider the semileptonic and nonleptonic $D_s$ decay modes to final states with $η$ and $η^\prime$. We use QCD sum rules to determine the $D_s \to η$ form factor $f_+^η$, and a generalized factorization ansatz to compute nonleptonic decays. We propose a parameterization of possible OZI suppressed contributions producing the $η^\prime$ in the final state, compatible with current data; such a scheme can be further constrained improving the precision of the measurement of the $D_s$ decay rates, as expected by the ongoing experiments.
We consider the weak decays of a B meson to final states that contain a S-wave radially excited vector meson. We consider vector-pseudoscalar final states and calculate ratios of the type $B \to ρ^{\prime} π/B \to ρπ$, $B \to ω^{\prime} π/B \to ωπ$ and $B \to ϕ^{\prime} π/B \to ϕπ$ where $ρ^{\prime}$, $ω^{\prime}$ and $ϕ^{\prime}$ are higher $ρ$, $ω$ and $ϕ$ S-wave radial excitations. We find such decays to have larger or similar branching ratios compared to decays where the final state $ρ$, $ω$ and $ϕ$ are in the ground state. We also study the effect of radial mixing in the vector system gen…
We study the flavor physics in two extensions of the quark sector of the Standard Model (SM): a four generation model and a model with a single vector--like down--type quark (VDQ). In our analysis we take into account the experimental constraints from tree--level charged current processes, rare Kaon decay processes, rare B decay processes, the $Z\to b \bar{b}$ decay, $K$, $B$ and $D$ mass differences, and the CP violating parameters $\frac ε^\prime}ε$, $ε_K$ and $a_{ψK}$. All the constraints are taken at two sigma. We find bounds on parameters which can be used to represent the New Physics con…
Decays of both $η$ and $η^\prime$ provide very useful information in our understanding of low-energy QCD, and experimental signatures for these decays would be extremely helpful at BES-III. The rare decays of the $η$ and $η^\prime$ mesons could serve as a low-energy test of the Standard Model and its beyond. The sensitivities of the measurements of $η$ and $η^\prime$ decays are discussed at BES-III, in which the $η$ and $η^\prime$ mesons are produced in the $ψ$ decays.
The rare $τ^- \to η^{(\prime)} π^- ν_τ$ decays, which are suppressed by $G$-parity in the Standard Model (SM), can be sensitive to the effects of new interactions. We study the sensitivity of different observables of these decays in the framework of an effective field theory that includes the most general interactions between SM fields up to dimension six, assuming massless neutrinos. Owing to the strong suppression of the SM isospin breaking amplitudes, we find that the different observables would allow to set constraints on scalar interactions that are stronger than those coming from other l…
In this article, we study the decays $ψ^{\prime}\to {J/ψ}π^+π^-$ and $η_c^{\prime}\to {η_c}π^+π^-$ by taking into account the chiral symmetry breaking effects, the final-state interactions and the heavy quark symmetry. We can confront the predictions of the $η_c^{\prime}\to η_c π^+π^-$ decay width and differential decay width with the experimental data in the future, and obtain powerful constraints on the chiral breaking effects and the final-state interactions, and test the heavy quark symmetry.
Rare $\vert Δc \vert=\vert Δu \vert=1$ processes uniquely probe flavor in the Standard Model and beyond from the up-type quark sector. Opportunities to search for BSM physics in charm arise from the severe GIM suppression which kills SM contributions to leptonic axial-vector contributions and suppresses CP violation. Semileptonic decays of charmed hadrons offer a variety of clean null test observables, featuring new physics effects which are even enhanced by resonance contributions. In particular, angular observables in three- and self-analyzing four-body baryon decays, such as $Λ_c\to p \ell^…
The rare processes $B_c\to D_{(s)J} ^{(*)}μ\barμ$, where $D_{(s)J}^{(*)}$ stands for the final meson $D_{s0}^*(2317)$, $D_{s1}(2460,2536)$,~$D_{s2}^*(2573)$, $D_0^*(2400)$, $D_{1}(2420,2430)$ or~$D_{2}^*(2460)$, are studied within the Standard Model. The hadronic matrix elements are evaluated in the Bethe-Salpeter approach and furthermore a discussion on the gauge-invariant condition of the annihilation hadronic currents is presented. Considering the penguin, box, annihilation, color-favored cascade and color-suppressed cascade contributions, the observables $\text{d}Br/\text{d}Q^2$, $A_{LPL}$…
Motivated by the first search for the rare charged-current $B$ decay to four leptons, $\ell \barν_\ell \ell^{(\prime)} \bar{\ell}^{(\prime)}$, we calculate the decay amplitude with factorization methods. We obtain the $B\to γ^*$ form factors, which depend on the invariant masses of the two lepton pairs, at leading power in an expansion in $Λ_{\rm QCD}/m_b$ to next-to-leading order in $α_s$, and at $\mathcal{O}(α_s^0)$ at next-to-leading power. Our calculations predict branching fractions of a few times $10^{-8}$ in the $\ell^{(\prime)} \bar{\ell}^{(\prime)}$ mass-squared bin up to $q^2=1~\text…
We point out new ways to search for charmless baryonic B decays: baryon pair production in association with $η^\prime$ is very likely as large as or even a bit larger than two body $Kπ/ππ$ modes. We extend our argument, in weaker form, to $B\to γ+ X_s$ and $\ellν+X$. Although calculations are not reliable, estimates give branching ratios of order $10^{-5}$--$10^{-6}$, where confidence is gained from recent experimental finding that $B \to D^{*} p \bar n$, $D^{*} p \bar p π$ are not far below $D^*π$ and $D^*ρ$ rates. Observation of charmless baryon modes would help clarify the dynamics of weak …
We probe the SUSY at the $10 \ {\rm TeV}$ scale in the rare decays and the CP violation of the kaon. We focus on the processes of $K_L \to π^0 ν{\bar ν}$ and $K^+ \to π^+ ν{\bar ν}$ combined with the CP violating parameters $ε_K$ and $ε_K^\prime/ε_K$. The Z-penguin mediated by the chargino loop cannot enhance $K_L \to π^0 ν{\bar ν}$ and $K^+ \to π^+ ν{\bar ν}$ because the left-right mixing of the stop is constrained by the $125$ GeV Higgs mass. On the other hand, the Z-penguin mediated by the gluino loop can enhance the branching ratios of both $K_L \to π^0 ν{\bar ν}$ and $K^+ \to π^+ ν{\bar ν…
We investigate the effect of scalar leptoquarks and family non-universal $Z^\prime$ boson on the rare leptonic decays of $B_{s, d}^*$ mesons, mediated by the FCNC transitions $b \to (d, s) l^+ l^-$. They are sensitive to a variety of new physics operators as opposed to the $B_{s,d}$ leptonic modes and hence, can provide an ideal testing ground to look for new physics beyond the standard model. We work out the constraint on new physics parameter space using the measured branching ratios of $B_{d, s} \to μ^+ μ^-$ processes and the $B_q - \bar B_q$ mixing data. Using the constrained parameters we…
We analyze patterns from CP-violating new physics (NP) in hadronic and semileptonic rare charm $\vert Δc \vert=\vert Δu\vert=1$ transitions. Observation of direct CP-violation in hadronic decays, as in $ΔA_{\text{CP}}$, provides opportunities for $c \to u \,\ell^+ \ell^-$, $\ell=e,μ$ transitions, and vice versa. For the concrete case of flavorful, anomaly-free $Z^\prime$-models a NP-interpretation of $ΔA_{\text{CP}}$ suggests measurable CP-asymmetries in semileptonic decays such as $D \to π\, \ell^+ \ell^-$ or $D \to ππ\, \ell^+ \ell^-$. Conversely, an observation of CP-violation in $c \to u\,…
In this work, we use the QCD sum rule method to study the radiative decays of the vector and axial-vector $B_c$ mesons to each of three charmed strange mesons, $D_s$, $D^*_s$ and $D_{s1}$, through their dominant weak annihilation channels. We calculate all relevant transition form factors, which are used to estimate the branching fractions at different channels. The order of branching ratios are obtained to be in the order of $ 10^{-6} - 10^{-5} $, which may be checked via differnet experiments.
Motivated by the large discrepancy of CP-violating phase in $\bar{B}_s-B_s$ mixing between the experimental data and the Standard Model prediction, we pursue possible solutions within a family non-universal $Z^{\prime}$ model. Within such a specific model, we find that both the $\bar{B}_s-B_s$ mixing anomaly and the well-known "$πK$ puzzle" could be moderated simultaneously with a nontrivial new weak phase, $ϕ^L_s\sim-72^{\circ}$ (S1) or $-82^{\circ}$ (S2). With the stringently constrained $Z^{\prime}$ coupling $B_{sb}^{L}$, we then study the $Z^{\prime}$ effects on the rare $B\to X_s μ^+μ^-$ …
We study impacts of dimension-five lepton-number violating operators associated with two same-sign weak bosons, $\ell^\pm \ell^{\prime \pm} W^\mp W^\mp$, on current and future experiments for neutrino oscillation, lepton-number violating rare processes and high-energy collider experiments. These operators can contain important information on the origin of tiny neutrino masses, which is independent of that from the so-called Weinberg operator. We examine constraints on the coefficients of the operators by the neutrino oscillation data. Upper bounds on the coefficients are also investigated by u…
Motivated by the recent observation of lepton universality violation in the flavour changing charged current transitions $b \to c l \barν_l$, we intend to scrutinize the lepton non-universality effects in rare semileptonic $B$ meson decays involving the quark level transitions $b \to u l \barν_l$. In this regard, we envisage the model-independent approach and consider the generalized effective Lagrangian in the presence of new physics and constrain the new parameters by using the experimental branching fractions of $B_u^+ \to l^+ ν_l$ and $B^- \to π^0 μ^- \bar ν_μ$ processes, where $l=e, μ, τ$…
We study the contribution of 2nd generation of quarks in NSIs. We investigate it through the rare decays of mesons involving neutrinos in the final state. We show the C and s quarks can effect NSIs just like u and s. We explore constraints on free parameter of NSIs. For this purpose we select 6 FCNC semi-leptonic processes of B, D and K mesons having neutrinos in the final state
Within the QCD factorization formalism, we study the possible impacts of the nonuniversal $Z^\prime$ model, which provides a flavor-changing neutral current at the tree level, on rare decays $B \to K_0^*π$. Under two different scenarios (S1 and S2) for identifying the scalar meson $K_0^*(1430)$, the branching ratios, CP asymmetries, and isospin asymmetries are calculated in both the standard model (SM) and the family nonuniversal $Z^\prime$ model. We find that the branching ratios and CP asymmetries are sensitive to weak annihilation. In the SM, with $ρ_A=1$ and $ϕ_A\in[-30^\circ, 30^\circ]$, …
We have carried out phenomenological implication of R-parity violating ($\NEG% {R}_{p}$) Minimal Supersymmetric Model (MSSM) via analyses of pure leptonic($% M\rightarrow ν\barν$) and semileptonic decays of pseudo-scalar mesons(% $M\rightarrow Xν\barν$). These analyses involve prediction of branching fraction of pure leptonic decays by using experimental limits/bounds derived from the study of semileptonic decays on $\NEG{R}_{p}$ parameters. We have found, in general that $\NEG{R}_{p}$ contribution dominates over the SM contribution i.e., by a factor of $10^{2}$ for the semleptonic decays of $…
The effects of final state interactions (FSI) in hadronic B-decays are investigated. The model for FSI, based on Regge phenomenology of high-energy hadronic interactions is proposed. It is shown that this model explains the pattern of phases in matrix elements of $B\toππ$ and $B\toρρ$ decays. These phases play an important role for CP-violation in B-decays. The most precise determination of the unitarity triangle angle $α$ from $B_d\to ρπ$ decays is performed. The relation between CP-asymmetries in $B\to Kπ$ decays is discussed. It is emphasized that the large distance FSI can explain the stru…
The $J/ψ$ weak decays are rare but possible within the standard model of elementary particles. Inspired by the potential prospects at the future intensity frontier, the $C$ parity violating $J/ψ$ ${\to}$ $πη^{({\prime})}$, $ηη^{\prime}$ decays and the strangeness changing $J/ψ$ ${\to}$ $πK$, $Kη^{({\prime})}$ decays are studied with the perturbative QCD approach. It is found that the $J/ψ$ ${\to}$ $ηη^{\prime}$ decays have relatively large branching ratios, about the order of $10^{-11}$, which might be within the measurement capability and sensitivity of the future STCF experiment.
Motivated by the recent measurement on ${\cal B}(\bar{B}_s\to ϕμ^+μ^-)$ by CDF collaboration, we study the effects of a family non-universal $Z^{\prime}$ boson on rare semileptonic $\bar{B}_s \to ϕμ^+μ^-$ decay. In our evaluations, we analyze the dependences of the dimuon invariant mass spectrum and normalized forward-backward asymmetry on $Z^{\prime}$ couplings and show that these observables are highly sensitive to new $Z^{\prime}$ contributions. Three limiting scenarios are presented in the detailed analyses. Numerically, within the allowed ranges of $Z^{\prime}$ couplings under the constra…
The decays of $η$ and $η^\prime$ mesons provide unique opportunities for testing the properties of low energy Quantum Chromodynamics and for the search of new physics beyond the Standard Model. However, recent experimental results on the rare decays of $η^{\left(\prime\right)}\rightarrowπ^0\left(η\right)γγ$ cannot be self-consistently described by the combination of the Vector Meson Dominance and Linear Sigma Model employing the same set of parameters. We show that this tension can be attributed to the presence of a leptophobic dark photon $\mathcal{B}$, and find representative values of the p…
Searching for heavy vector bosons $Z^\prime$, predicted in models inspired by Grand Unification Theories, is among the challenging objectives of the LHC. The ATLAS and CMS collaborations have looked for $Z^\prime$ bosons assuming that they can decay only into Standard Model channels, and have set exclusion limits by investigating dilepton, dijet and to a smaller extent top-antitop final states. In this work we explore possible loopholes in these $Z^\prime$ searches by studying supersymmetric as well as leptophobic scenarios. We demonstrate the existence of realizations in which the $Z^\prime$ …
The rare top quark decays mediated by a new neutral massive gauge boson that is predicted in models with extended gauge symmetries are studied. We focus on the processes $t\to cV, uV$ induced at the one loop level, where $V =γ, g$, by considering different extended models. It is found that, within a broad range of mass of the new neutral gauge boson, the models predict branching ratios for the decays in study that are competitive with respect to the corresponding branching ratios in the standard model. In order to establish bound on our branching ratios, we consider the recent experimental bou…
Motivated by the recent anomalies in $b \to s \ell^+ \ell^-$ transitions, we explore a minimal $Z^\prime$ scenario, in which the $Z^\prime$ boson has a flavour-changing coupling to charm and top quarks and a flavour-conserving coupling to muons. It is found that such a $Z^\prime$ boson can explain the current $b \to s \ell^+ \ell^-$ anomalies, while satisfying other flavour and collider constraints simultaneously. The $Z^\prime$ boson can be as light as few hundreds GeV. In this case, the $t \to c μ^+ μ^-$ decay and the $tZ^\prime$ associated production at the LHC could provide sensitive probe…
We analyze rare charm baryon decays within the standard model and beyond. We identify all null test observables in unpolarized $Λ_c \to p \ell^+ \ell^-$, $\ell=e, μ$ decays, and study the new physics sensitivities. We find that the longitudinal dilepton polarization fraction $F_L$ is sensitive to electromagnetic dipole couplings $C_{7}^{(\prime)}$, and to the right-handed 4-fermion vector coupling $C_{9}^\prime$. The forward-backward asymmetry, $A_{\rm FB}$, due to the GIM-suppression a standard model null test already, probes the left-handed axialvector 4-fermion coupling $C_{10}$; its CP-asy…
The final state interactions (FSI) model, in which soft rescattering of low mass intermediate states dominate, is suggested. It explains why the strong interaction phases are large in the $B_d\toππ$ channel and are considerably smaller in the $B_d\toρρ$ one.
We calculate the leading power corrections to the decay rates, distributions and hadronic spectral moments in rare inclusive \bxsll decays in the standard model, using heavy quark expansion (HQE) in $(1/m_b)$ and a phenomenological model implementing the Fermi motion effects of the b-quark bound in the B-hadron. We include next-to-leading order perturbative QCD corrections and work out the dependences of the spectra, decay rates and hadronic moments on the model parameters in either HQE and the Fermi motion model. In the latter, we take into account long-distance effects via $B \to X_s +(J/ψ, …
$U(1)^\prime$ extensions of the standard model with generation-dependent couplings to quarks and leptons are investigated as an explanation of anomalies in rare $B$-decays, with an emphasis on stability and predictivity up to the Planck scale. To these ends, we introduce three generations of vector-like standard model singlet fermions, an enlarged, flavorful scalar sector, and, possibly, right-handed neutrinos, all suitably charged under the $U(1)^\prime$ gauge interaction. We identify several gauge-anomaly free benchmarks consistent with $B_s$-mixing constraints, with hints for electron-muon …
Decays of the lightest neutralino are studied in R_p-violating models with operators lambda^{prime} L Q D^c and lambda L L E^c involving third-generation matter fields and with dominant lambda^{prime} and lambda couplings. Generalizations to decays of the lightest neutralino induced by subdominant lambda^{prime} and lambda couplings are straightforward. Decays with the top-quark among the particles produced are considered, in addition to those with an almost massless final state. Phenomenological analyses for examples of both classes of decays are presented. No specific assumption on the compo…
